Round balers generally have a bale forming chamber defined by an array of side-by-side belts, transverse slats trained on chains, a plurality of rolls or a combination of these various elements, e.g., rolls and belts. During field operation, crop material such as hay is picked up from the ground and fed into a fixed or adjustable diameter chamber. The hay is then rolled into a compact cylindrical package, wrapped with twine, net or the like and ejected onto the ground for subsequent handling.
Many balers of the type mentioned above employ automated or semi-automated systems to control one or more of the operational steps. It is common for these systems to include arrangements for varying the desired size of bales formed in the bale forming chamber. A successful arrangement of this type is disclosed in U.S. Pat. No. 4,167,844, issued Sep. 18, 1979 in the name of John H. Freimuth, et al, wherein an automatic twine wrapping apparatus is contemplated in which a triggering mechanism is actuated in response to a selected bale size in the forming chamber. Upon actuation, control means initiate automated steps of a twine wrapper including application of twine around the bale, severing the twine when the wrapping function is completed and resetting the system for the next wrapping operation.
In the patent mentioned above the apron take up arms move in response to change in bale size, i.e., the arms move as hay is being formed into a cylindrical package in the bale forming chamber. Take up arm position is monitored and used to initiate tripping of the mechanism that controls the wrapping apparatus. Other prior art balers have also used the position of the take up arms to initiate wrapping. For example, in U.S. Pat. No. 5,014,613, issued May 14, 1991 in the name of John H. Merritt, et al, a round baler of the type that uses rolls and belts to define the bale forming chamber is disclosed in which a twine wrapping trip mechanism is responsive to the position of the belt take up mechanism.
Both of the above mentioned balers are exemplary of prior art twine wrapper trip mechanisms with control systems that utilize linkages for coupling the take up arms to the control for the trip mechanism. Adjusting such systems for selecting bale size requires physical changes of the relationship of the elements.
Although prior art round baler twine wrapper control mechanisms for adjustable bale size have met with varying degrees of success, there is always a need for a less complicated and inexpensive system that enhances the overall operation of the round baler which in turn results in an improvement in overall performance and reliability of the machine.